Transparent films which display information are widely used throughout many different industries and for many applications. Typically, a positive image is formed by placing an ink or pigment onto a transparent plastic sheet. The image is then displayed by projection or by light transmission.
Many methods are available for printing a positive image onto a transparent plastic sheet. Ink jet printers, and their associated ink formulations, are well advanced technically; and aqueous ink jet printers represent a respectable share of the total printing market. Aqueous ink jet printing is particularly advantageous for printing text or images where the printed area covers a small portion of the area of the transparent sheet. However, aqueous ink jet printing is less suitable for printing large areas of a transparent plastic sheet since a large volume of solvent must be removed from the media. The volume of solvent increases with image density which leads a skilled artisan away from ink jet printing for high optical density, large print area applications.
Phase change ink printing corrects many of the deficiencies of aqueous ink jet printing. A high optical density can be obtained and large areas can be printed without evaporation of solvent. The impact of phase change ink printing in the market place has been impeded due to the lack of a suitable transparent media. Media designed for use with aqueous or other solvent based ink jet printers is unsuitable due to the large coating weight of the ink receptive layer which is required to absorb the ink solvent. Furthermore, the coatings used for aqueous or solvent ink jet media do not provide adequate adhesion for the phase change ink composition. Thus, there is a need for a media which will take full advantage of the properties offered by phase change ink printing.
Compositions described in commonly assigned U.S. Pat. No. 5,756,226 demonstrate adequate performance when used with phase change ink jet printing methods. Improvements in ink adhesion are still desired to insure adequate adhesion between the ink and the media. An overcoat comprising a softer polymer mixture is demonstrated herein to provide superior adhesion.
Japanese unexamined Patent Appl. Kokai 6-32046 teaches the addition of up to 10%, by weight, of a zirconium compound to improve the print quality. Japanese unexamined Patent Application Kokai 4-364,947 utilizes TiO.sub.2 in a similar manner. The transparency of the coated layer is compromised by the addition of zirconium or titanium solids rendering the film unsuitable for use as a transparent media. Japanese unexamined Patent Appl. Kokai 4-201,286 teaches media which is suitable for aqueous ink jet printing yet the surface is susceptible to scratching. High scratch susceptibility renders a media unacceptable for use in automatic printing devices and for high quality printing applications.